The present invention relates to medical methods and systems. More particularly, the invention relates to a method and system for physiological gating.
Many types of medical procedures involve devices and machines that act upon a particular portion of a patient body. For example, radiation therapy involves medical procedures that selectively expose certain areas of a human body, such as cancerous tumors, to high doses of radiation. The intent of the radiation therapy is to irradiate the targeted biological tissue such that the harmful tissue is destroyed. In certain types of radiotherapy, the irradiation volume can be restricted to the size and shape of the tumor or targeted tissue region to avoid inflicting unnecessary radiation damage to healthy tissue. Conformal therapy is a radiotherapy technique that is often employed to optimize dose distribution by conforming the treatment volume more closely to the targeted tumor.
Other medical procedures are also directed to specific portions of a patient body. For example, radiation imaging typically directs radiation only to the portion of a patient body to be imaged. 3-dimensional imaging applications such as computed topography (CT), PET, and MRI scans also are directed to specific portions of a patient body.
Normal physiological movement represents a limitation in the clinical planning and delivery of medical procedures to a patient body. Normal physiological movement, such as respiration or heart movement, can cause a positional movement of the body portion undergoing treatment, measurement, or imaging. With respect to radiation therapy, if the radiation beam has been shaped to conform the treatment volume to the exact dimensions of a tumor, then movement of that tumor during treatment could result in the radiation beam not being sufficiently sized or shaped to fully cover the targeted tumoral tissue. For imaging applications, normal physiological movement could result in blurred images or image artifacts.
One approach to this problem involves physiological gating of the medical procedure, such as gating of a radiation beam during treatment, with the gating signal synchronized to the movement of the patient's body. In this approach, instruments are utilized to measure the physiological state and/or movement of the patient. Respiration has been shown to cause movements in the position of a lung tumor in a patient's body; if radiotherapy is being applied to the lung tumor, then a temperature sensor, strain gauge, preumotactrograph, or optical imaging system can be utilized to measure the patient during a respiration cycle. These instruments can produce a signal indicative of the movement of the patient during the respiratory cycle. The radiation beam can be gated based upon certain threshold amplitude levels of the measured respiratory signal, such that the radiation beam is disengaged or stopped during particular time points in the respiration signal that correspond to excessive movement of the lung tumor.
Many approaches to physiological gating are reactive, that is, these approaches utilize gating methods that slavishly react to measured levels of physiological movements. One drawback to reactive gating systems is that the measured physiological movement may involve motion that that is relatively fast when compared to reaction time of the imaging or therapy device that is being gated. Thus, a purely reactive gating system may not be able to react fast enough to effectively gate the applied radiation. For example, the gating system may include a switch or trigger for gating radiation which requires a given time period Δt to fully activate. If the delay period Δt is relatively long compared to the measured physiological motion cycle, then a system employing such a trigger in a reactive manner may not be able to effectively gate the radiation at appropriate time points to minimize the effect of motion.
Therefore, there is a need for a system and method to address these and other problems of the related art. There is a need for a method and system for physiological gating which is not purely reactive to measure physiological movement signals.
The present invention provides an improved method and system for physiological gating. According to one embodiment, gating is performed based upon visual detection of patient motion relating to physiological activity. In an embodiment, an optical-based system is employed to measure and record physiological patient movement, in which a camera tracks and views the movement of a marker block or marker(s). A method and system is also disclosed for detecting and predictably estimating regular cycles of physiological activity or movements. Another aspect of an embodiment of the invention is directed to predictive actuation of gating system components. Yet another aspect of the invention is directed to physiological gating based upon the phase or non-periodicity of the physiological activity. The present invention can also be used to gate, either prospectively or retrospectively, any type of procedure, including radiation therapy or imaging, other types of medical devices and procedures such as MRI, PET, SPECT, and CT scans.
An embodiment of the invention also provides a system and method for position and motion monitoring including prompting the patient to hold breath and monitoring of the breath-hold state of the patient. In one embodiment, a patient positioning system comprises at least one camera, a marker block, and a computing device to compute the location and orientation of the marker block. The marker block preferably comprises a plurality of landmarks, e.g., retro-reflective markers. According to an embodiment, a method for identifying the position of a patient comprises the steps of first co-locating the marker block with a patient, viewing the marker block with at least one camera, producing image coordinates for the identified landmarks viewed by the camera, comparing the image coordinates with reference coordinates for the landmarks, and thereafter determining the position and orientation of the patient.
Consistent patient positioning, either within the same device for different sessions, or between multiple devices, is facilitated using an optical-based positioning system, according to one embodiment of the present invention. Within the same device, the positioning system provides absolute position information for the patient that can be re-created during each treatment session. Between multiple devices, the optical-based positioning system establishes relative positioning information for the patient. The relative positioning information can be used to correctly conform the position of the patient between multiple devices. In one embodiment, a patient undergoes treatment planning at a first device during which an optical positioning system identifies a first relative position for the patient. Thereafter, the patient is controllably positioned to a therapy device, e.g., using a movable treatment table or in which the patient remains stationary but either the treatment planning or therapy device are moved in relation to the patient, e.g., on rails. The relative position of the patient to the therapy device is established and manipulated to conform to the desired treatment strategy.
The present invention also provides a novel method and mechanism for implementing a physiological monitor, such as a respiration monitor. In one embodiment, a physiological monitor is implemented using an optical-based system in which a video camera records body movement relating to the physiological activity being monitored. The image data relating to the body movement is processed and displayed to represent the physiological movement. The movement data can be analyzed and viewed to monitor the physiological activity.
User interface inventions are disclosed for controlling and displaying motion, positioning, and gating information. In one embodiment, a circular interface is provides to control gating or treatment intervals based upon phase of physiological movement. Interface embodiments of the invention provide display and control for enabling/disabling gating and establishing gating thresholds. Additional interface embodiments display breath hold parameters and physiological motion range information.
One embodiment of the invention provides a method and mechanism for video and/or audio prompting of patients to maintain desired physiological movement patterns. A disclosed embodiment employs a slider image that simultaneously displays visual feedback of the physiological movement as well as a desired range of the movement. For respiration activity, the slider comprises a movable slider bar that moves in response to a patient's inhale-exhale movements. This provides visual prompting and feedback regarding the respiration activity. In an embodiment, verbal prompting are employed to assist in controlling, maintaining, or manipulating the physiological activity of interest. For respiration activity, such verbal promptings could be computer-activated prompting to instruct a patient to breath in and breath out.
These and other aspects, objects, and advantages of the invention are described below in the detailed description, drawings, and claims.